Why does a gas generator bog down when under increased electrical load

I would like to understand the reasoning behind why a gas powered generator bogs down, as if strained or restricted when an increased electrical load is placed on the generator.

It's all a function of speed. The generator wants to maintain a 60 Hz output frequency. All generators, barring the use of special settings, have what is called a load droop characteristic. To electricians and electrical engineers they are known as "House Curves". These curves relate real load, measured in kilowatts, to output frequency and reactive load, measured in kilovolt-amperes, to output voltage. They are direct relations. In this case, we look at the real load-frequency relation. When load is increased, it will slow the machine down and lower the output frequency; the frequency droops with load. The voltage regulator on the machine, despite its name, when operating in an automatic mode, will strive to maintain the constant output frequency. Therefore, as load is increased, the voltage regulator will force the machine to speed up to maintain the 60 Hz output. The bogging down of the machine that you hear is the lag time between the load increase and the speeding up of the machine, as the it takes time for the fuel injectors to open up and provide more firing power to the engine. It is very similar to the bogging down of your vehicles engine when transitioning from a flat surface to an incline.

Gasoline engine powered generators use a governing mechanism to maintain a throttle opening
which is adequate to maintain engine speed under load. If the the governor is defective, or the load is excessive (beyond the generator's rating); engine speed will fall.
This is true only for generators which must maintain 3600 rpm engine speed to produce 60 cycle AC power
Simply speaking, an electrical load makes the generator harder for the engine to turn.
The additional load is analogous to a car climbing a hill. It will require more throttle opening (power) to maintain a constant speed.

When the electrical load is increased the generator applies more torque to the gasoline engine. The gasoline engine will bog down for a moment until the engine's governor increases the fuel to the engine. This causes the engine's speed to increase.
A generator converts mechanical energy into electrical energy, and it in turns applies a force back on the engine that must be overcome by the gasoline engine.

Lets simplify it. When driving uphill don't you have to push the gas pedal further down! It's simply relative to torque vs motion.